Mooney_Driver wrote:
Not to forget prevailing winds! There is hardly a point installing an ILS on a runway which might have 2-3 days per year wind which would make its use necessary.
Funnily enough, there are a few airports right here in CA where exactly that is the case. One of them being San Louis Obispo (KSBP) that has an ILS to rwy 11, whereas the prevailing winds are from the west 90% of the time. I have never managed to figure out why that’s the case, but suspect something to do with obstacles.
Edited to add: KSBP used to have a BC approach to rwy 29, but that has now been withdrawn and replaced with an RNAV (GPS) approach. I did fly this BC during IR training but AFAIK it was the only one in SoCal.
I think it’s terrain. An ILS needs a long straight approach which in the case of KSBP is over the ocean.
KMRY (Monterey) is the same, the ILS is in the wrong direction 95% of the time, but it comes in over the ocean. And it’s a long runway, so you can generally land downwind if you have to (did that once, ILS almost to minima and below circling minima).
Now KMRY has an RNP approach which wiggles round over the terrain, but that’s relatively recent.
PANS-OPS does not mention BC approaches at all. I’ve checked the list of amendments and there is no mention of BC having been removed, so it looks like PANS-OPS has never included BC approaches.
It won’t need other specs than those for LOC, offset LOC or in worst cases an LDA (localiser but designed like circling), the only thing is max FAF recommended distance being closer (to stay within operational coverage, say the runway is +2NM long)
172driver wrote:
I have never managed to figure out why that’s the case, but suspect something to do with obstacles.
We have that in LSZR, Altenrhein. Runway 28 has two “obstacles” in the way: a) a bunch of hills to the east which would have had to make the GS steeper than usual and b) the neighbourly Austrians who put a restricted area in place to block the airport. B was with certainty the foremost reason an instrument approach to 28 was never even attempted.
I wonder if they still would feel that way today… but the R-area still exists and so does the contract between the two countries.
So, after all this, does anyone know why Europe has no BC approaches?
Ibra wrote:
It won’t need other specs than those for LOC, offset LOC or in worst cases an LDA (localiser but designed like circling), the only thing is max FAF recommended distance being closer (to stay within operational coverage, say the runway is +2NM long)
Most certainly it needs other specs! For one thing the transmitter is located differently in relation to the runway. Another thing is that it is not obvious to me that the precision will be the same on the back lobes.
Peter wrote:
So, after all this, does anyone know why Europe has no BC approaches?
I’d be willing to be it’s because BC is not in PANS-OPS so not an ICAO standard approach procedure.
Airborne_Again wrote:
For one thing the transmitter is located differently in relation to the runway
Yes signal precision is not the same but sometime even in DC LOC transmitters are allowed to be located differently in relation to the runway or threshold but not sure about max the offset tolerances? in any case the specs for signal tolerances, obstacles & minima tolerances they should be like those of LOC, offset LOC or LDA
Or why it can’t be treated like (“timed back-course”) NPA on VOR/NDB: the one where you cross the nav aid and leave it behind your back on final? France has load of them: Beauvais, Deauville for VOR and Annecy, Bergerac for NDB…they are useless (unsafe unless you hand fly them 6 times per month) but very cheap: you only need one single NAV Aid few nm from the airport and DME or stopwatch for the MAPT
Annecy have removed their BC LOC but they kept NDB RWY04 (timed flown on the tail), you gotta be really brave to leave an NDB 7nm behind your back with a clock and 4 mountains ahead !
Remote NDB approaches are just a huge joke, unless you happen to be currently flying one. The math is simple. Suppose your compass is accurate to 1 degree. And suppose you can fly a heading accurately to within 1 degree. Both fairly improbable in reality, but let’s suppose. Suppose also that the NDM is 5 NM off the field. Then on average you can expect to be 500 feet laterally within the runway when you break out. If you’re at 500 feet vertically, that is HUGE. You’re expecting the runway to be somewhere let’s say within the windshield pillars, not way off to one side.
So “traditional” single-NDB approaches are OK for 2000 foot minima, but nothing much lower than that.
That said, on my IFR checkride (20 years ago) I broke out and the runway was right in front of me. Not sure who was more surprised, me or the examiner.
johnh wrote:
If you’re at 500 feet vertically, that is HUGE. You’re expecting the runway to be somewhere let’s say within the windshield pillars, not way off to one side.
You are describing the view I had the last time I flew one in France for real down to 400ft, more in 0.5nm region along the downwind, since then I went for GPS (pretty impressive piece of technology: no issue hand flying it down to 10ft along the runway center line), one can’t afford to be stupid & lucky twice, I should have gone with my first IRI advice: get your IR test done then leave the NDB to cricket games 
